1. Field of the Invention
The present invention relates to a developing unit, a process cartridge, and a developing cartridge for developing images using developing agent.
2. Description of Related Art
A conventional image forming device includes a known developing unit that develops electrostatic latent images into visible images using charged particles of toner. This type of developing unit can leak toner. The leaked toner can stain the interior of the image forming device and recording sheets, thereby degrading printing quality. The leaked toner can also stain the user""s hands or clothes during replacement of the developing unit.
One such developing unit with this problem includes a developing roller and a layer thickness regulating blade. The developing roller transports toner on its surface, and the layer thickness regulating blade regulates the toner on the surface of the developing roller to a thin layer. The layer thickness regulating blade includes a stainless steel plate spring and a rosin or rubber pressing member, both formed to the same length in their lengthwise direction. Non magnetic single component developing agent is used as toner. The toner easily leaks from around the edges of the developing roller as the developing roller rotates.
Conventionally, various configurations have been provided inside the developing unit in order to prevent toner leakage. As will be described next, side seals, a lower film and sponge seal members are examples of configuration provided for preventing toner leakage.
The side seals are formed from a urethane sponge with a Teflon(trademark) felt attached thereto. The urethane sponge needs to be sufficiently soft and have a low compression set. The side seals are positioned on opposite sides of the layer thickness regulating blade, near one or the other end of the developing roller. The side seals are disposed in sliding frictional contact with the peripheral surface of the developing roller to prevent toner from leaking around the lengthwise ends of the developing roller. The Teflon(trademark) felt can be pressed with sufficient pressing force against the developing roller, without increasing rotational torque required for rotating the developing roller. The sides seals also pressingly contact the layer thickness regulating blade so as to pressingly sandwich the blade therebetween, in order to prevent toner from leaking out between the layer thickness regulating blade and the side seals.
The side seals of one type of developing unit are provided with their side surfaces pressed against the pressing member of the layer thickness regulating blade. However, with this configuration, toner can easily leak from between the layer thickness regulating blade and the side seals.
The side seals of another type of developing unit are disposed with one edge in contact with the free edge of the layer thickness regulating blade. That is, assuming that the layer thickness regulating blade extends downward and the pressing member is at the lowermost end of the blade, then the upper edge of the side seals presses against the lower edge of the pressing member. With this configuration, toner can be prevented from leaking initially. However, over a long period of use, fiber from the Teflon(trademark) felt of the side seals can press up the pressing member and enter between the layer thickness regulating blade and the developing roller. As a result, a gap can open between the pressing member and the developing roller. Toner can leak out through the gap.
Either of these configurations involves a trade off between toner leaks and sufficient pressing force between the side seals and the layer thickness regulating blade. That is, if the side seals press against the pressing member with a force sufficient for preventing toner from leaking, then the side seals can interfere with the function of the layer thickness regulating blade. The pressing force from the side can prevent the thickness regulating blade from uniformly pressing against the developing roller, especially at the end portions of the developing roller. As a result, the layer thickness regulating blade cannot provide a uniform-thickness toner layer on the developing roller. However, when the pressing force blade is reduced to prevent such interference, toner can leak from between the side seal and the layer thickness regulating blade.
The lower film is for preventing toner from leaking between the developing roller and the portion of the developing unit casing below the developing roller. The lower film is maintained in sliding frictional contact with the developing roller at this location. The lower film is usually made from urethane rubber or a polyethylene terephthalate (PET) sheet. Although the urethane rubber provides a sufficiently soft pressing force, it has insufficiently low stiffness on its own, and so needs to be pressed from behind by a sponge or other member. The PET sheet is stiffer than the urethane rubber film and so does not need to be pressed from behind by a sponge member. Therefore, the PET sheet makes assembly processes easier than does the urethane rubber film.
The sponge seal members are also for preventing toner leaks from between the thickness regulating blade and the developing unit casing. The sponge seal members are disposed near lengthwise ends of the layer thickness regulating blade, between the developing unit casing and the rear surface of the layer thickness regulating blade, that is, the surface of the layer thickness regulating blade that faces away from the developing roller. One surface of each sponge seal member is attached to either the layer thickness regulating blade or the developing unit casing by two-sided tape. The opposite surface of the sponge seal member is pressed against the other of the layer thickness regulating blade and the developing unit casing by pressure alone.
The thickness regulating blade itself also functions to prevent toner leakage. Because the thickness regulating blade presses against the developing roller, it prevents toner from leaking between the developing roller and the opening in the developing unit casing.
However, the layer thickness regulating blade vibrates in association with rotation of the developing roller. This vibration is sufficient for producing gaps between the sponge seal member and either the layer thickness regulating blade or the developing unit casing, whichever in not adhered to the sponge seal member. Polymerized toner, which has excellent fluidity, can easily leak through those gaps.
Moreover, the toner can also leak through other sealed areas wherein a sponge seal member merely presses against surfaces of other configurations that vibrate in association with rotation of the developing roller.
It is an objective of the present invention to reliably prevent toner from leaking between side seals and the layer thickness regulating blade, while maintaining proper pressing force between the layer thickness regulating blade and a developing roller.
It is another objective of the present invention to reliably prevent toner from leaking between the developing unit casing and components that can potentially vibrate even slightly.
To achieve the above-described objectives, a developing device according to the present invention for developing a latent static-electric image into a visible image from developer, includes a developing case, a developer bearing body, a developer layer thickness regulator, and contact members.
The developing case is for holding developer, and is formed with an elongated opening.
The developer bearing body is disposed in the opening of the developing case, with lengthwise ends of the developer bearing body rotatably supported on the developing case.
The developer layer thickness regulator includes a pressing member and a plate spring member. The pressing member is formed from rubber or resin and extends in a lengthwise direction of the developer bearing body. The plate spring member supports the pressing member pressingly against an outer periphery of the developer bearing body to form a thin layer of developer on the developer bearing body. The plate spring member extends in the lengthwise direction of the developer bearing body to a longer length than the pressing member. Also, the pressing member is separated from the lengthwise ends of the plate spring member. Therefore, end portions of the plate spring member are left uncovered by the pressing member.
The contact members each slidingly contact a corresponding peripheral surface of the developer bearing body near a corresponding lengthwise end of the developer bearing body. Each contact member is attached to a corresponding one of the end portions of the plate spring member and extends to cover the corresponding end portion.
According to this aspect of the present invention, it is desirable that base seals be additionally provided. In this case, the base seals are attached to the developing case, each facing a corresponding peripheral surface of the developer bearing body near a corresponding lengthwise end of the developer bearing body. Each contact member further extends to a corresponding base seal and is attached to the corresponding base seal. It is desirable that base seals be formed from a resilient foam material.
According to this aspect of the present invention, it is desirable that resilient foam seals be additionally provided. In this case, each resilient foam seal is interposed between a corresponding end portion of the plate spring member and a corresponding contact portion. The contact portions are attached to the corresponding end portion of the plate spring member through a corresponding base seal. It is desirable that the pressing member contacts each resilient foam seal along a length of 4 mm or greater.
According to this aspect of the present invention, it is desirable that the pressing member be formed from silicon rubber.
According to this aspect of the present invention, it in desirable that the pressing member have conductivity.
According to this aspect of the present invention, it is desirable that the developer bearing body is a resilient roller having conductivity.
According to another aspect of the present invention, a developing device for developing a latent static-electric image into a visible image of developer, includes a developing case, a developer bearing body, a member, a case-side seal, and a member-side seal.
With this aspect of the prevent invention also, the developing case is for holding developer and the developing case is formed with an opening.
Also, the developer bearing body is supported in the opening at lengthwise ends by the developing case.
The member vibrates in association with rotation of the developer bearing body.
The case-side seal is made from a resilient foam material attached to the developing case.
The member-side seal is made from a resilient foam material attached to a surface of the member and in abutment with the case-side seal.
According to this aspect of the present invention, it is desirable that the member be an elongated developer layer thickness regulator disposed with a front surface thereof pressed against an outer periphery of the developer bearing body to form a thin layer of developer on the developer bearing body. The elongated developer layer thickness regulator has a rear surface facing opposite from the front surface. The member-side seal in attached near a lengthwise end of the developer layer thickness regulator on the rear surface of the developer layer thickness regulator.
The developing case can be formed with a seal attachment surface and a regulator attachment surface, wherein the developer layer thickness regulator is positioned on the regulator attachment surface to resiliently press the case-side seal and the member-side seal in a thickness direction of the case-side seal and the member-side seal. The seal attachment surface is receded from the regulator attachment surface in the thickness direction by a step portion that extends from the seal attachment surface and that is located adjacent to ends of the developer layer thickness regulator and the member-side seal. With this configuration, it is desirable that an end seal formed from a resilient foam member be attached to the step portion in contact with the end of the case-side seal. It is desirable that the case-side seal be attached to the developing case in pressing contact with the end seal, and that the end seal have a thickness in a non-compressed condition of 2 mm or less.
According to both of the above-described aspects, it is desirable that the developer be a polymerized toner formed by polymerization techniques.
According to both of the above-described aspects, it is desirable that a static electric latent image bearing member be provided, and that the developing case include a process cartridge case that houses the static electric latent image bearing member.
According to both of the above-described aspects, it is desirable that a process cartridge case be further provided. In this case, the developing case is adapted for free attachment and detachment with respect to the process cartridge case.
According to both of the above-described aspects, it is desirable that an image forming device be further provided. In this case, the developing case is adapted for free attachment and detachment with respect to the image forming device.